Actually a gurad page is a part of a stack vma and we don't want to remap
it by a restorer vma.

The crtools on restore find a place for a restorer vma, which will not
intersect with other VMAs. A guard page is a part of a stack VMA, if
we don't take into account it, we can place the restorer VMA on it and
that case is a bug.

Would not this lead to situation where we expand stack manually? Every new
c/r cycle add one page to the bottom of stack, no? No:

strace:
mmap(0x5f4d0e0cc000, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS|MAP_GROWSDOWN, -1, 0) =
0x5f4d0e0cc000

/proc/PID/maps:
5f4d0e0cd000-5f4d0e0cd000 rw-p 00000000 00:00 0
.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>